Critical parameters and risk evaluation index for spontaneous combustion of coal powder in high-temperature environment

In thermal powered direct blow coal powder manufacturing at high-temperatures, the mechanism and key parameters of the spontaneous combustion of coal powder are not clear, which makes the prevention of such spontaneous combustion difficult. Therefore, the spontaneous combustion of coal powder for different oxygen concentrations (oxygen concentrations of 5, 7, 9, 13, 17, 21%) and volumes (21, 200, 300, 400, and 500 cm3) in a high-temperature environment was studied experimentally by the physical similarity simulated experimental appliance. The results indicate that when the oxygen concentration in the coal powders from the LHG sample (Liuhuanggou mine coal sample) and Hongliu mine coal sample (HL sample) samples was higher than 13% and 9%, respectively, the temperature of the center-point rises rapidly beyond other conditions. As the temperature increases, the concentrations of the CO and C2H4 gases increase gradually and the CO/CO2 ratio increases exponentially. However, the C2H4/C2H6 ratio is unstable when the temperature is lower than 180°C, beyond which it gradually increases. The minimum ignition temperature of the coal powder increases gradually with the decrease in the oxygen concentration, and the ignition delay time is also prolonged considerably.